The present invention relates generally to image processing systems and more particularly to image processing systems which determine statistical moments associated with each pixel of the image.
Image processing systems often calculate values for the mean and moments of each pixel of a rectangular array of pixels that comprise an image scene. The mean and moments (centered moments) are calculated for a sliding window centered on every pixel in the image, with the resulting mean and moments assigned to the center pixel position. For example, a typical image size might be 256 by 256 pixels with a sliding window size of 15 by 15 pixels. Considering a sliding window comprised of 225 pixels, the mean of the 15 by 15 array of pixels is given by the equation x=1/N.SIGMA.x.sub.i, where x.sub.i represents the intensity of the ith pixel, N is the total number of pixels in the sliding window, and the summation is from i=1 to N, and represents the summation over all pixel elements of the window. For purposes of statistical analysis, the mean (x) may be considered equivalent to the first centered moment of the sliding window. The higher order centered moments are determined from the equation Mk= 1/N.SIGMA.(x.sub.i -x).sup.k, where x represents the mean, and k is the particular moment being determined.
In prior art systems, to calculate one of the moments for a single pixel it was necessary to take the signal value in each pixel, subtract the mean from each value, raise the resulting value to the correct power, sum all 225 values in the sliding window, and then divide by 225. This represents 450 additions and 225 multiplications per pixel. In a typical television image situation, there are 65,536 pixels in each image and each image lasts 1/60th of a second. This results in a computation rate of about 2.6.times.10.sup.9 calculations per second for each moment, neglecting computation of the mean.
It is clear, considering the voluminous number of calculations required to determine each of the centered moments, that it would be an improvement in the art to have a system which provides for a reduction in the number of calculations required to produce these computations.